Felted, lignocellulose products and method of making the same



July 31, 1956 c. c. HERITAGE 2,757,115 FELTED, LIGNOCEILLULOSE PRODUCTSAND METHOD OF MAKING THE SAME Filed Jan. 30, 1955 3 Sheets-Sheet 1INVENTOR. Clark C. Her-1' i'c1 c -e y 1956 c. c. HERITAGE 2,757,115

FELTED, LIGNOCEJLLULOSE PRODUCTS AND METHOD OF MAKING THE SAME 3Sheets-Sheet 2 Filed Jan. 30, 1953 INVENTOR.

. Herifczge CJark C y 1956 c. c. HERITAGE 2,757,115

FELTED, LIGNOCELLULOSE PRODUCTS AND METHOD OF MAKING THE SAME 3Sheets-Sheet 3 Filed Jan. 30, 1955 m w w.

Clark C. Hem i'c ge ES 1.... a

United States Patent FELTED, LIGNO'CELLULOSE PRODUCTS AND METHOD OFMAKING THE SAME Clark C. Heritage, Tacoma, Wash., assignor, by directand mesne assignments, of one-half to Weyerhaeuser Timber Company,Tacoma, Wash, a corporation of Washington, and one-half to WoodConversion Com pany, St. Paul, Minn., a corporation of DelawareApplication January 30, 1953, Serial No. 334,162 9 Claims. (Cl. 154101)This invention relates to felted, lignocellulose products, and tomethods of making the same.

In the manufacture of hardboard and related products, lignocellulosematerials such as wood, corn stalks, bagasse, straw, and the like,conventionally first are reduced to the form of small pieces. These areformed or felted into a predetermined shape which then is consolidatedto the preselected density by the application of heat and pressure.

In this procedure, the quality and properties of the hardboard producedfrom a given lignocellulose material are determined by six principalfactors, namely (1) the physical form of the lignocellulose particles,(2) the physical and/or chemical treatment to which the lignocellulosehas been subjected prior to, during or after its reduction to the formof small particles, (3) the character and amount of materials added tothe lignocellulose particles for such purposes as improving the strengthand water resistance of the final product, (4) the type of forming orfelting operation employed, (5) the conditions of pressing, and (6) anypost-pressing treatment such as tempering or humidification. Of these,the physical form of the lignocellulose particles, the physical andchemical treatment to which the lignocellulose has been subjected, andthe character of the felting operation are fundamental in determiningthe properties of the final product. If any one of these factors isneglected, no amount of improvement of the other variables will besuccessful in producing a hardboard of the maximum possible propertyvalues. It is to these factors that the present invention is directed.

Although hardboard heretofore has been made by many different processes,the properties of the product have not been as good as they might havebeen for failure properly to control one or more of the foregoing threefundamental variables. The lignocellulose particles have been used, forexample, in either non-fibrous or fibrous physical forms. If innon-fibrous form, as where they comprise sawdust, wood flour, groundwood, shavings, or chips, the hardboard produced therefrom necessarilyis of inferior quality since the particles of which it is composed,because of their shape and dimensions, cannot be intertwined and formedinto a coherent felt prior to consolidation. As a result, theconsolidated product is deficient in strength, a deficiency which canonly partially be compensated for by the addition of relatively largeproportions of binder. Also, where sawdust, wood flour, ground wood andother materials having large, porous surface areas are used, asubstantial loss of binder occurs through impregnation of the particles.

When a fibrous lignocellulose starting material is employed, theforegoing diificulties are in large measure obviated because wood andother lignocellulose fibers may be intertwined and formed into acoherent felt having strength properties which are reflected inincreased strength of the consolidated product. However, wood is adifiicult material to reduce to the form of fibers, i. e.

to the form of single tracheids, since the fibers which comprise thewood structure are breakable, and are bound together into a tough,coherent mass by the noncellulosic content of the wood. Hence, anyagency which is sufficiently potent to separate the fibers from eachother, is also likely to break the fibers transversely. Also, it isdifficult to reduce the material substantially completely to the form ofindividual fibers and as a result a large proportion of non-feltable,rigid, woody bundles and wood chunks are obtained.

Thus in one conventional defibering process, green or kiln-dried wood iscombed or raked along the grain with steel brushes to separate thefibers. This necessarily mutilates and breaks the fibers transversely sothat fiber fragments and chunks are obtained as the principal finalproducts.

In another conventional defibering process, wood chips are rubbedbetween serrated metal discs. This method, like the combing procedure,sufiers from the fundamental disadvantage that in order to separate thefibers from each other so much force is employed that the fibers arebroken, and as a result fiber fragments, or a mixture of fiber fragmentsand woody chunks are obtained as products. To overcome this ditficulty,the chips often are subjected to a prior treatment with steam orchemicals to soften them prior to defibering, but this also isdisadvantageous, as will be pointed out hereinafter.

In still another widely employed defibering operation, wood chips aresubjected to the action of steam at very high temperatures andpressures. After this the pressure is suddenly released whereupon thewood is exploded to fiber form. This process has the inherentdisadvantage, however, of over-treating the material with subsequentdegradation of its substance.

Turning now to the second fundamental variable which is of primarysignificance in determining the properties of a hardboard product, itagain is noted that the properties of the lignocellulose may bedeleteriously affected by subjecting it to the action of steam and otherchemical agents before, during or after its defibration. Thus in theprocess described above wherein wood chips are subjected to a prolongedsteaming procedure in order to soften them for defibration, thelignocellulose substance is hydrolyzed and thermally degraded.

This occurs because of the insulating qualities of the wood. In order tosoften the chips, they must be treated with high temperature steam untilthe interior of the chips has been heated sufiiciently to soften andplasticize the lignin. As a consequence, the outer portions of the chipsare overheated and pyrolyzed. This degrades the wood fiber, adverselyaffecting its strength. It also converts a substantial proportion of thewood substance to water soluble materials which may be lost insubsequent processing operations, if at any time the fiber is suspendedin an aqueous conveying medium.

Similarly, the same processes of degradation and solubilizing occur inthe explosion process for defibering wood, but to even a greater degree.In this process the steam temperature and pressure employed are so highthat the wood substance is scorched and darkened. This limits its use tothe manufacture of dark colored products. It also weakens the fiber, aresult which can only partially be compensated for by the addition ofextraneous binder. Still further, it makes the fibers dead andnon-resilient and causes them to lose a substantial measure of theirability to bind themselves together upon. being pressed. In addition, asmuch as one-third of the total wood substance is converted to watersoluble materials which may be lost if the fibrous product at any timeduring its processing is contacted with a substantial volume of water.

The third of the above noted factors which are fundamental incontrolling the properties of the final product is the character of theoperation by which it is formed into a mat or a felt prior to pressing.In general, there are two processes for accomplishing this result. Inthe wet process, a water slurry of the fiber is formed, which is passedon to a screen to drain off the water, following the orthodox papermaking technique.

This procedure is undesirable for several reasons. It requires elaborateand costly machinery. It Washes out the water solubles which maycomprise a large proportion of the wood substance and which contributein substantial degree to the bonding together of the fibers when theyare pressed. Disposal of the white water creates a serious problem. Theconveying water washes out some of the added binder and size, ifpresent. The felts produced are heavy with water and difficult tohandle. Because of their moisture content, they cannot be stored,transported or otherwise treated before being consolidated in ahot-press. The high moisture content of the felt markedly increases theheat usage during pressing, and correspondingly increases the cost ofthat operation. Satisfactory laminated felts cannot be produced. Undercertain conditions the fibers tend to orient themselves in the machinedirection as the felt is laid and hence a felt of randomly oriented,intertwined fibers is not formed. Also, the necessarily high density ofthe wet mat prevents random orientation of the fibers.

The dry or moist felting technique wherein dry or moist fibers aredeposited in a mat or felt from a conveying medium comprising a gas suchas air overcomes many of the foregoing difficulties. It employs simpleequipment and obviously does not remove the soluble content of thefibers. Furthermore, any additive materials, such as extraneous binders,may be deposited efliciently upon the fibers and are not washed outsubsequently in the white water, as occurs in appreciable degree in thewet process.

However, most of the conventional air laying operations wherein thefibers are permitted to gravitate onto the supporting member also haveinherent disadvantages. In the first place, it is difiicult to coat thefibers uniformly with binder where such is used. This is because in theabsence of a suspending liquid, the binder is not deposited uniformly onthe fiber surfaces. Also, the fibers tend to agglomerate and form clumpsor fiocs, and this leads to the production of a non-uniform felt.

Secondly, many of the air laid forms are hard to handle since they areloosely felted and not bonded and hence tend to disintegrate. Also, thesurface fibers may not be anchored into the mat so that they blow awayin air currents prior to pressing, and are easily rubbed off afterpressing.

Thirdly, in some of the dry felting procedures, it is difficult to forman integral, multiple-layer felt, having for example, coarse fibers inthe interior and fine fibers on the exterior. This is because condiionsare not right for mixing and inter-locking the interfaced fibers of thelaminae to form an integrated structure. As a result, the felt and theconsolidated product derived therefrom are subject to delamination.

It is the essence of the present invention that the foregoingdifficulties are overcome and a consolidated product of demonstrablysuperior properties is produced by using a fibrous starting material ofselected physical form, produced while being subjected to carefullycontrolled non-degrading treating conditions, and felted by a pneumatic,impact-felting technique. As a result, all three of the above discussedfundamentally important variables are controlled to give optimum resultsso that a superior hardboard product may be made from a selectedlignocellulose starting material.

This result is achieved by a novel process which basically comprisesdefiberizing the lignocellulose by rubbing and abrading it whilesubjecting it to an atmosphere of steam maintained at from about 50 toabout 200 pounds per square inch gauge for from about A minute to about30 minutes. This produces a moist, fibrous product which consistsprimarily of discrete, whole, single tracheids and flexible opened upbundles of the same. The fibers having a water content insufficient toprovide a fluid suspension of a mass of such fibers then are entrainedin a stream of air or other gaseous vehicle and driven against aforaminous support member. This forms a felt containing impacted, drivenfibers in which the individual fibers are randomly oriented andintertwined by the driving force of the entraining vehicle. The mat thenmay be consolidated by the application of heat and pressure to form thefinal hardboard product, wherein the driven fibers add to the strengthand integrate the body to nonlaminar form.

Considering the foregoing in greater detail and with particularreference to the drawings wherein:

Fig. l is a schematic view of the apparatus employed for preparing thefibers used in the preparation of the herein described consolidatedproduct;

Fig. 2 is a schematic view of the felting apparatus which may beemployed in forming a felt from the fibers produced in the apparatus ofFig. 1;

Fig. 3 is an enlarged detail view of the felting head assembly employedin the felting apparatus of Fig. 2;

Fig. 4 is a photograph, enlarged 40 times, of the herein described fiberas prepared from Douglas fir wood;

Fig. 5 is a photograph similar to Fig. 4, enlarged 15 times andillustrating a conventional fiber made by defibering steamed Douglas firchips between serrated metal discs; and

Fig. 6 is a photograph, enlarged 15 times, of a felt made from the fiberof Fig. 4 using the hereindescribed pneumatic, impact-felting technique.

In accordance with the present invention lignocellulose, which maycomprise corn stalks, bagasse, straw and the like, but preferablycomprises wood in the form of chips, is introduced into bin 10. It isfed from this bin by means of a screw conveyor 12 into the horizontal,steam heated preheater 14 of the defibrator. The latter may be of anysuitable construction wherein the lignocellulose is rubbed and abradedwhile being contemporaneously subjected to the action of steam.Preferably, however, it comprises the defibrator known as the Asplunddefibrator, substantially as described in U. S. latent 2,145,851 toAsplund. The preheater of this machine has on its infeed side aconstriction 16. It is fed with steam under pressure through line 18,which may also introduce steam into the defibrating chamber.

The chips after traversing the horizontal preheater pass into thevertical preheater 20, whence they are forced through the spool piece 22into the defibrating chamber 24. There, having been softened by thesteam environment present in the apparatus, they are fed betweenrelatively rotatable discs 26, 28, which rub and abrade them to form afibrous product consisting principally of ultimate fibers in the form ofindividual tracheids, together with a minor proportion of flexiblebundles of fibers. This result is achieved because when the chips aredefibered in a steam environment it is not necessary to heat each chipuntil it is entirely heated through, thereby degrading the woodsubstance. Rather, the surface of each chip is heated until the ligninis softened, whereupon the surface fibers are rubbed off by thedefibering discs. This exposes a new surface which then is softened bythe steam environment and further reduced to fibers by the action of thediscs. This sequence continues until the chips have been entirelyreduced to fibers, which are removed from the region of high pressureand temperature substantially as soon as they are formed so that theyare not deteriorated thereby.

In order to obtain the desired result during defibering, i. e. thereduction of the lignocellulose to the form of individual tracheids witha minor proportion of flexible bundles of the same without chemicallydegrading the wood, it is necessary to control the conditions within thedefibrator within carefully defined limits, which mayvary for eachspecific material. These conditions are met when wood chips aredefibered while subjecting them to an atmosphere of steam maintained atbetween about 50 and about 200 pounds per square inch gauge, andcorresponding temperatures for saturated steam, for periods of timeranging from about A minute to about 30 minutes, the lower limit of thepressure-temperature range applying to the higher limit of the timerange. Pre ferred conditions are between about 80 and about 160 poundsper square inch gauge for from about /2 minute to about 6 minutes. Whenthe lignocellulose is defibered under these conditions, a majorproportion of substantially ultimate fibers or individual tracheids areproduced with a minimum of degradation of the wood substance.

The fibrous product formed in the defibrating chamber is dischargedthrough an orifice 30 which creates a plug of fiber at the outfeed sideof the machine. This together with the plug formed at constriction 16 onthe infeed side maintains the desired pressure.

The discharged fiber enters a first conduit 32 atv substantially themachine temperature and in a moist condition, its moisture content beingbetween about 30% and about 100% by Weight (dry basis). Since it hasbeen forced suddenly from a region of relatively high pressure to one ofsubstantially atmospheric temperature, there is a marked lowering of thetemperature as a result of the instantaneous and therefore nearadiabatic expansion of the steam. The heat thus liberated assists indrying the fibers.

Also, the fibers are in a condition of great turbulence and maytherefore now be mixed effectively with additive materials. Hence, athermosetting resinous binder, if such is to be incorporated, may beintroduced in a pumped, metered feed through line 34. Other materials,such as thermoplastic binders, sizing materials, fire-proofing agentsand the like, may be introduced at this point, as well as at otherpoints, as for example, in the preheater, via line 36, or ahead of thedefibrating discs via line 38.

Suitable thermosetting resins for use in conjunction with the presentlydescribed process comprise the ureaformaldehyde resins, themelamineresins, and the phenolaldehyde resins including thethermosetting, resinous condensation products of phenol andformaldehyde, phenol and acetaldehyde, phenol and furfural, the cresolsand formaldehyde, resorcinol and formaldehyde, etc.

A fast curing thermosetting resin which is particularly suitable for usein this process is the phenol-formaldehyde resin having aformaldehyde-phenol ratio of about 1.5-3 to 1, i. e. one prepared usingfrom about 1.5 to about 3 mols of formaldehyde for each mol of phenol.In addition, it may be characterized by the following approximateproperties:

Viscosity (cp. at 25 C.) 100-1000 Specific gravity at 25/25 C 1.14-1.16Percent alkalinity (NaOH) 2-6 Non-volatile content (percent) 30-50 Theseand other thermosetting resins may be employed singly or in admixturewith each other in amounts of between about 0.1% and about 15%,preferably between about 2% and about 6% by weight based on the dryweight of the fibrous composition.

Where a thermoplastic-resin is employed alone or with a thermosettingresin, it may be used in amount of between about 2% and about 60%,preferably between about and about 40% by weight, based on the dryWeight of the fibrous composition. A variety of thermoplastic resinsthus may be employed, suitable ones being the asphalts, the gilsonites,the pine wood resins including extracted pine wood pitch (Vinsol), thethermoplastic natural gums such as Congo gum, the thermoplasticcellulose ethers, the thermoplastic cellulose esters, the

fraction indicating a substantial thermoplastic polyvinyl chlorides andacetates, and the like.

In order to dry the moist mixture of fiber and binder as well as toadvance the thermosetting resin to the opti mum extent without renderingit inert and infusible, the fiber-binder mixture formed just beyondorifice 30 is passed rapidly through the elongated conduit 32 Where itis thoroughly mixed, cooled by the expansion of the steam as well as byradiation from the conduit, partially dried, and its resin content onlypartially cured because of the short duration of passage through theconduit. From conduit 32 the mixture passes through steam separator 40where some further cooling may occur, after which it enters a secondconduit 42.

The latter communicates with a heating chamber 44' supplied with air orother dehydrating gases, such as nitrogen or flue gas, heated ifnecessary in heater 46 and forced into the conduit by means of fan 48.The air supplied by this heater is at a temperature sufiicient to raisethe temperature of the mixture to a level at which it is dried to avalue of between about 5% and about 40%, preferably to between about 10%and about 30% by weight. It also etfectuates a further advancement ofthe resin, but without destroying its bonding and fusible qualities.

When it is to be used as felting stock, the dried mixture may beseparated from the entraining air in cyclone 50 where it is cooledrapidly. This prevents further advancement of the resin. The fiberproduct with or without added resin then is deposited on conveyor 52 forconveyance to storage, or to the felting means, or to a fiberfractionating means 54. The latter may be a series of vibrating screens,a winnower, or one or more whizzers (Crites U. S. Reissue 20,543) andhas for its function the division of the fiber product into a pluralityof size fractions. One such fraction may be a relatively smallproportion of fines, which may be discarded. Another fraction may becoarse particles, which may be discarded, recomminuted in a secondrefiner, or recycled via conduit 56 to hopper 10 for feeding again intothe defibrator. Still another fraction may be the bulk of the materialwhich constitutes the acceptable fraction for the purposes of thepresent invention. The acceptable fraction passes in a conduit 58, to aconduit 59 which conveys it to the felting apparatus. Conduit 58 mayalso receive run of the machine fiber from conveyor 52 when this isdesired and when conveyor 52 is run in the appropriate direction.

By the foregoing procedure there is obtained the fiber product which isuniquely suited for the felting operation described below. In the firstplace, the fiber is in the form of single tracheids or flexible openedup bundles of thesame, as is illustrated in Figure 4. This figure is tobe compared with Fig. 5, which illustrates a conventional fiber preparedby defibering previously steamed chips between mechanical discsoperating under atmospheric con ditions. It is at once apparent that theconventional product contains a high proportion of sticks, ribbons andchunks. Furthermore it contains a relatively high proportion of fiberfragments. From this it is clear that even if this fiber is fractionatedto remove the sticks, ribbons and chunks, the remaining product willconsist not primarily of individual tracheids and flexible, opened upbundles of the same, as in the case of applicants products, but ratherof a large proportion of fiber fragments which do not have desirablefelting qualities, as will be more fully developed hereinafter.

The desirable properties of the presently described acceptable fractionof fibers for fiberboard manufacture are further indicated by theirparticle size distribution, compressive properties and feltability. Asmeasured in a Clark Classifier, less than 5% falls in the plus 8 meshabsence of chunks and large particles, while less than 25% falls in theminus fraction, indicating that only a relatively minor proportion offines is present and of this proportion a major fraction consists ofsmall, whole fibers. The fibers have, furthermore, a high resistance tocompression, a typical value being about 80 pounds per square foot (seeAnway U. S. 2,325,026). This indicates the fiber to be live and springyso that it may be felted efficiently to form a strong, coherent felt.Feltability tests to be described in detail hereinafter indicate thisfelt to have a tensile strength of about double that of a felt made fromthe same wood species which has been steamed and then defibered atatmospheric pressure to a fiber designed for felting to mats for hotpressing to hardboard.

The presently described defibering process thus produces a fibrousproduct which is uniquely suited for use in the production offiberboard. This is because of all fiber types, it most nearlyapproaches natural wood in its properties, while still being produciblein high yield, This is a direct result of the defibering operation whichpermits separation of the individual tracheids from each other underconditions so mild as to inhibit the formation of degradation productsof the lignocellulose, such as an unduly large proportion of watersolubles and particularly of products which hide or darken the Woodcolor. Such water solubles as are formed, moreover, are retained by thefiber, thereby increasing the yield of fibrous prodnot and supplying anative binder available for bonding in subsequent consolidatingoperations.

The native binder present may be reinforced and supplemented by thepresence of added binder introduced at a suite le stage, preferablyduring the defibering operation in one or more of the ways describedabove. This enables utilizing the binder in the most efficient manner,spreading it over the fiber surfaces as opposed to impregnating thefibers, and in the case of a thermosetting binder, advancing it to theoptimum point for a rapid pressing schedule. Still further, the fibercontains a very high proportion of flexible, resilient individualtracheids and flexible aggregates of the same, all of which may beintertwined and interlocked to form a coherent, strong, felt ofdemonstrably superior qualities.

In order to take advantage of the foregoing desirable qualities of thepresently described fibrous product, however, the ensuing feltingprocedure must be so designed as to preserve and utilize them. Thus isshould not degrade the fibers by subjecting them to the action ofexcessive heat or strong chemical agents. Also, it should not removefrom them the desirable content of water solublematerials.

Still further, the felting procedure should be so designed as to takeadvantage of the physical form of the fibers, intertwining andinterlocking them with each other to form a strong coherent felt whichmay be handled easily. Then upon pressing the felt the fibers arepressed and bonded to form a pressed product which is remarkably strongbecause of the inherent strength developed through interlocking of thefibers as well as through the adhesive forces developed by the nativeand added binder.

it is another fundamental aspect of the present inven tion that theabove desiderata are achieved by felting the fibers using a pneumatic,impact felting technique, which will be described below with particularreference to Figures 2 and 3.

In accordance with the illustrated embodiment, the acceptable fractionof fiber from fiber fractionator 54 is conveyed via conduit 59 to belt60. This belt has associated with it a weighing mechanism 62., so thatthe combination comprises a weighing feeder for feeding a measuredamount of fiber into a hopper 64.

Hopper 64 communicates with a conduit 66 having therein a chute 68,positioned for feeding additive material such as extraneous size orbinder. The additive materials are fed to chute 68 by means of asuitable weighing and feeding mechanism including the weighing unit 70which deposits the additive upon a conveyor 72, which in turn emptiesinto chute 68.

Suction is applied to conduit 66 by means of a rotary fan 74 whichdrives the mixture of fiber and additives through an elongated conduit,76 where mixing of the fiber with the additives occurs. Conduit 76 inturn empties into a housing 78 which serves as an expansion conduit forthe air-entrained fibrous mixture.

Hence, it serves the functions of reducing the velocity of the fibers,minimizing felting in the housing, and of equalizing the air stream overthe discharge area of the housing. Accordingly, housing 78 flaresdownwardly through increasing rectangular cross-sections as by means ofa pyramidal structure. In practice, housing 7% may flare from arectangular cross-section at the bottom opening of about 24 x 54 inchesin a vertical drop of about 17 feet.

The bottom or discharge opening of housing 78 may be extended by asuitable tubular means such as headbox 30. The length of the head-boxmay be varied to suit particular installations, since it serves as aconnecting link between housing 78 and the felting head 82 connected tothe head-box at its discharge end.

Felting head 32 comprises a semi-cylindrical member disposedsubstantially at right angles to the machine direction. A suitable arc,for example, an arc of about 100, of its periphery is perforatedsymmetrically with openings 84 having a diameter calculated to passindividualized fibers of the air-entrained fibrous mass fed theretounder pressure from fan 74. in practice, when felting wood fibers, thediameters of these openings may be from -7 to inch in diameter andcounter-sunk deeply from the exterior side. The openings thus serve thefunction of breaking up any fiber clumps and of passing a uniform rainof individual fibers to the exterior. The countersinking minimizes theextent of cylindrical wall in the openings, thereby minimizing thetendency of the holes to plug during fiber delivery and to deliver slugsfelted within the holes.

To assist in breaking up the fiber clumps and transmitting them throughthe openings in the felting head, there is provided agitating meanswhich in a preferred embodiment comprises the paddle-wheel 86 mountedcoaxially with the felting head and driven by a suitable power means.

The individual fibers passing through perforations 34 are driven in asteady stream by the force of the entraining air against a foraminoussupport member which preferably is a moving, continuous screen 90.Screen 90 is driven by suitable means at a rate correlated with the rateof deposition of the fibers to form a felt of the desired thickness.

The felting of the fibers on screen bi is assisted by establishing avacuum beneath the screen. To this end there is provided a suction box@2 of suitable dimensions. It communicates with a conduit M which inturn leads to a fan 96, which exhausts through conduit 98 into a solidsseparator such as cyclone fltitl. The latter serves the function ofseparating any finely divided materials which may have passed throughscreen 90. These then are reintroduced into the feed by transferringthem into hopper 64 where they are mixed with the fresh feed.

The fibers then are formed into a continuous, uniform mat or felt 102 bythe co-action of the driving force of the pressure stream in the feltinghead above the screen and the suction stream in the suction box belowthe screen. It will be apparent that the felting conditions are subjectto a certain degree of variation in order to accommodate various fibertypes and to build felts of preselected characteristics.

Such variation may be accomplished, for example, by varying the ratio offeed to entrained air, the speed of rotation of rotor 86, the dimensionsof the felting area, the relative pressures of the pressure and vacuumstreams, and the like. in general, however, in order to achieve thedesired result of driving the felting fibers into the partially formedfelt to secure the critically necessary random the following example:

orientation and intertwining of the fibers, the conditions should beadjusted so that the fibers are traveling at a velocity of between about100 and about 1500 feet per minute in the region directly above thescreen. This is achieved by maintaining a pressure of from about 0.1 to1.0 inches of water in the head-box and a pressure of from about 2 toabout 30 negative inches of water in the suction box.

Felt 102 is contained within and dimensioned laterally by a pair ofopposed vertical side walls, one of which is indicated at 104, stationedon opposite sides of the screen and connected by a vertical end wall106.

After the felt leaves the forming area it passes between the pressingrollers 108, 110 which effect a partial consolidation and make the feltself-sustaining. Thence it passes to a conveyor 116, past side trim saws118 and beneath an automatic cut-off saw 120, which moves angularlyacross the moving mat to cut rectangular sections therefrom of theselected length. These sections then pass to a conveyor 122, over blade124 and thence to a conveyor 126. The latter conveyor moves at adifferent rate than do the preceding conveyors in order to separate thefelt sections. These then are transferred to caul plates, preferablyplaced on the stretch of conveyor 126 below conveyor 122, and thereafterconveyed to the press indicated schematically at 130. i i

The pressing conditions are somewhat variable depending upon the type offiber employed, the thickness of the product to be produced, themoisture content of the felt, the character of any resinous binder whichmay be present therein, the density and surface characteristics desiredin the final product, and the like. In general, however, when making A3inch hardboard from a felt having a moisture content of between about 5%and about 40% by weight, the felt may be pressed at from about 120 toabout 250 C. at a pressure of between about 50 and about 1000 pounds persquare inch for a time of between about 2 and about minutes.

From the foregoing it is apparent that the superior properties which arecharacteristic of the fibers produced by the present process are in noway deleteriously-affected by the felting procedure. Furthermore, thefelting operation is of a character such as to make the best possiblefelt from the fibers. This is attributable to the fact that the fibersfirst are entrained in an air stream and then impacted or drivenindividually toward the felting screen. This effect is clearly apparentfrom Figure 6.

It will be noted from this view that the fibers, initially resilient,curly, individualized, and retaining substantially their originallength, lie at all angles to each other. Some of them lie in thehorizontal plane, some at an angle thereto, and some in the verticalplane. The latter may be considered as nailers" holding together themore horizontally disposed fibers. All of the fibers are intertwined andinterlocked with each other to form a coherent mat. This effect isfurther evidenced by the fact that the felt may be flexed and evenrolled up on itself without surface cracking or interior delamination.

It is evident that when this mat is consolidated by the application ofheat and pressure, the randomly oriented fibers will be crirnpedtogether and locked in those position by the native and added binder toform a fiberboard product of maximum strength for the given rawmaterials.

Also, the product is characterized by superior bendability,

making possible the fabrication of severely and permanently contouredobjects without delamination.

The presently described process is illustrated further in ExampleDouglas fir wood chips were defibered in an Asplund machine regulated toprovide a steam environment of 140 pounds per square inch gauge and acorresponding temperature for saturated steam. The dwell time of thechips within the machine was about 1 minute.

About 1% phenol-formaldehyde resinous binder eniployed in the form of analkaline aqueous solution having a resin solids content of about 40% anda pH of about 11 was introduced just downstream from the orifice of themachine. The resulting fibers were dried to a moisture content of 25% byweight.

As a control, there was obtained a quantity of Douglas fir wood fibermanufactured by steaming whole wood chips at a steam pressure of about60 pounds per square inch gauge and a corresponding temperature forsaturated steam for a time period of about 30 minutes. The steamed chipsthen were transferred to an Allis-Chalmers Interplane Grinder set toproduce the maximum proportion of individual fibers obtainable from thisdevice. The fibrous product then was dried to a moisture content ofabout 15%.

The two products were compared as to appearance, particle sizedistribution, bulk density, compressive properties, and feltability. Thecomparison as to appearance already has been discussed above inconnection with Figures 4 and 5, the predominance of ultimate fibers andthe relative absence of woody chunks, slivers and ribbons in thepresently described fiber again being noted. The comparative particlesize distributions in percent by weight of the two products asdetermined by a Clark Classifier were as follows, the values being meshsizes:

Present Control Fraction fiber fiber (percent) (percent) From acomparison of the above values it becomes apparent immediately that runof the machine fiber as produced by the presently described process isalmost entirely free of the +8 fraction, which contains substantiallyall of the large non-fibrous particles which are undesirable for thepresent purposes. The control fiber, on the other hand, contained over21% of this fraction.

A comparison of the fiber lengths of the two products is given below:

that Douglas fir wood fibers have a maximum length of about 7 mm. Itthen becomes apparent that in the case of the present fiber 83% of theproduct had a particle length of 7 mm. or less and of this 78% was inthe form of ultimate fibers. In the case of the control fiber, although81% had a length of 7 mm. or less, only 38% was in the form of ultimatefibers. Hence it is clear that the presently described defiberingprocess produces an amount of ultimate fibers which is more than doublethat produced by the most closely competitive defibering procedure.

A comparison of the unimpacted bulk densities of the two fibrousproducts revealed that the present fiber had a bulk density of 1.34pounds per cubic foot, while that of the control fiber was 1.27 poundsper cubic foot.

Comparison of the compressive properties of the two products indicated aresistance to compression of 81.0 pounds per square foot for the presentfiber and a resistfor the control fiber. These values indicate that thepresent fiber is a more resilient, feltable material than is thecontrol. i

In comparing the feltability qualities of the two products an impactedmat was formed using a sufficient thickness of fiber to produce aone-eight inch board having a density of 64 pounds per cubic foot. Thismat was compressed at room temperature and 600 pounds per square inchfor 1 minute. The tensile strength of a 6-inch wide strip of theresulting felt then was determined immediately. The felt formed from thepresent fiber had a tensile strength of 11.3 pounds While the controlfiber had a corresponding strength of only 6.6 pounds, thereby againillustrating the inherent strength present in the felts made inaccordance with the present invention.

The two fibrous products then were made into hardboard by entraining thefibers in a stream of air at a fiber velocity of about 200 feet perminute in accordance with the process described above using a pressurein the felting head of about .40 inch of water and a pressure in thesuction box of about 5.7 negative inches of water. The felts then werepressed at 750 pounds per square inch and 200 C. for 8 minutes and themodulus of rupture of the two fiberboard products determined. Thepresently described fiber produced a hardboard having a rupture modulusof 6900 pounds per square inch, while the control fiber pro duced ahardboard having a rupture modulus of only 5500 pounds per square inch,these values being corrected to a density of 64 pounds per cubic foot.

Furthermore, the presently described fiber produced a hardboard ofremarkably improved bending properties. This was indicated by theresults of comparative bending tests carried out on the instanthardboard, as well as on four currently marketed commercial products.The tests were carried out by soaking the hardboard sheets in water forvaried periods of time and thereafter bending them to a 135 angle on aconventional bending machine having a 3.5 inch roll diameter. Theresults are summarized in the following table.

form of individual tracheids which are curly, elongated, resilient, andfree from chunks and slivers. This product is obtained with minimumtransverse breakage of the fibersand without subjecting them to anydegrading chemical treatment which weakens the wood structure, causesthe fibrous product to lose life, and which results in the production ofan inordinate amount of water soluble materials. The relatively smallamount of the latter substances which are produced by the presentprocess are fully retained and spread on the fiber surfaces where theyserve as a valuable native binding agent.

Still further, the character of the felting operation is such as toutilize to the greatest extent possible the desirable felting qualitiesof the fiber employed. Thus, as has been fully brought out hereinabove,the fibers are impacted into a felt in random orientation and with theindividual fibers intertwined and interlocked. Hence, as is fullyapparent from the superior strength obtained for the presently describedhardboard product, the superior qualities and strength of the felt arereflected in a corresponding improvement in the final pressed productwith the result that for the first time a hardboard has been producedwhich may be manufactured in large volume and in which are developed tothe maximum degree the desirable properties of products of this class.

Having now described my invention in preferred embodiments, I claim asnew and desire to protect by Letters Patent:

1. The process of making consolidated fibrous products which comprisesdefiberizing lignocellulose by rubbing and abrading it whilecontemporaneously subjecting it to an atmosphere of steam maintained atfrom about to about 200 pounds per square inch gauge and correspondingtemperatures for saturated steam for periods of time ranging from aboutA minute to about 30 minutes, the lower limit of thepressure-temperature range applying to the higher limit of the timerange, fractionating the fibrous product thus produced at a moisturecontent of from about 5% to about 40% to effect separation of thePresently described Commercial Hardboard Commercial Hardboard CommercialHardboard Commercial Hardboard Hardboard #1 #2 #3 #4 Presoaking 7 BreakSur- Angle, Break Sur- Angle, Break Sur- Angle, Break Sur- Angle, BreakSur- Angle, face degrees face degrees face degrees ce degrees facedegrees 35 min 0 1 134 0 1- 2 128 129 X 3 113 X 133 0 1 122 X 1. 5 108121 X 114 X 127 3 sec 0 3 134 X 118 126 X .1 117 X 132 N orn.-XSignifiessample broke in bending; 0-Signifies no breakage during bending;l-Signifies satisfactory surface; 2Signifies marginal suriaceuseful forlimited applications; 3Signifies unsatisfactory surface.

The foregoing tests indicate that the hardboard of the present inventionis characterized by several fundamentally improved bendingcharacteristics. It is easier to bend than are the competitivehardboards, requiring a much shorter presoaking period. It may be bentto a sharper angle and once bent, has a reduced tendency to spring back.The surface at the bend is improved on both the tension and compressionsides of the board in that the surface is smoother and less subject todelamination. The board is stronger at the bend. Also, it may be bentequally well in random direction as opposed to some boards which may bebent in one direction only depending, for example, upon the orientationof the fibers. These properties are clearly attributable to the factthat in the production of the hereindescribed hardboard prodnot asuperior fiber first is provided which then is felted prior to pressinginto a mat wherein the fibers are intertwined and interlocked, therebypermitting bending withcut breaking, delamination or weakening of theboard.

From the foregoing it will be apparent that by the present inventioncontrol has been achieved for the first time over the three fundamentalvariables which must be regulated in order to obtain a hardboard ofmaximum quality. Thus a fiber starting material has been produced in thefibrous product into a plurality of size fractions, one of whichconsists primarily of discrete whole ultimate fibers and flexible openedup bundles of the same having a particle size in the range of from +8 to80 mesh particles as measured by a Clark Classifier and contains lessthan 5% of the +8 and less than 25% of the -80 mesh particles,entraining the said fraction in a moving gaseous vehicle, driving thecomponent fibers while so entrained against a fcraminous support member,thereby forming a mat of impacted fibers in which the individual fibersare randomly oriented and entrained by the driving force of theentraining vehicle, and consolidating the resulting mat by theapplication of heat and pressure.

2. The process of claim 1 in which the 'fiber velocity in the entrainingmoving gaseous vehicle is between about and about 1500 feet per minute.

3. The process of making consolidated fibrous products which comprisesdefiberizing lignocellulose by rubbing and abrading it whilecontemporaneously subjecting it to an atmosphere of steam maintained atfrom about 50 to about 200 pounds per square inch gauge andcorresponding temperatures for saturated steam for periods oftime'ranging from about A minute to about 30 minutes, the lower limit ofthe pressure-temperature range apply- 13 1 ing to thehigher limit of thetime'irange, mixing with the fibrous product thus produced from about0.1% 'to about 15 by weight of thermosetting resin, fractionating theresulting fibrous product at a moisture content of from about to about40% to effect separation of the fibrous product into a plurality of sizefractions, one of which consists primarily of discrete whole ultimatefibers and flexible opened up bundles of the same having a particle sizein the range of from +8 to 80 mesh particles as measured by a ClarkClassifier and contains less than 5% of the +8 and less than 25% of the+80 mesh particles, entraining the said fraction in a moving gaseousvehicle, driving the component fibers while so entrained against aforaminous support member thereby forming ,a mat of impacted fibers inwhich the individual fibers are randomly oriented and entrained by thedriving force of the entraining vehicle, and consolidating the resultingmat by the application of heat and pressure.

4. The process of making consolidated fibrous products which comprisesdefiberizing lignocellulose by rubbing and abrading it whilecontemporaneously subjecting it to an atmosphere of steam maintained atfrom about 50 to about 200 pounds per square inch gauge andcorresponding temperatures for saturated steam for periods of timeranging from about A minute to about 30 minutes, the lower limit of thepressure-temperature range applying to the higher limit of the timerange, mixing with the fibrous product thus produced from about 2% toabout 60% by weight of thermoplastic resin, fractionating the resultingfibrous product at a moisture content of from about 5% to about 40% toeffect separation of the fibrous product into a plurality of sizefractions, one of which consists primarily of discrete Whole ultimatefibers and flexible opened up bundles of the same having a particle sizein the range of from +8 to 80 mesh particles as measured by a ClarkClassifier and contains less than 5% of the +8 and less than 25% of the80 mesh particles, entraining the said fraction in a moving gaseousvehicle, driving the component fibers While so entrained against aforaminous support member thereby forming a mat of impacted fibers inwhich the individual fibers are randomly oriented and entrained by thedriving force of the entraining vehicle, and consolidating the resultingmat by the application of heat and pressure.

5. The process of making consolidated fibrous products which comprisesdefiberizing lignocellulose by rubbing and abrading it whilecontemporaneously subjecting it to an atmosphere of steam maintained atfrom about 50 to about 200 pounds per square inch gauge andcorresponding temperatures for saturated steam for periods of timeranging from about ,4 minute to about 30 minutes, the lower limit of thepressure-temperature range applying to the higher limit of the timerange, mixing with the fibrous product thus produced from about 0.1% toabout by weight of thermosetting resin and from about 2% to about 60% byweight of thermoplastic resin, fractionating the resulting fibrousproduct at a moisture content of from about 5% to about 40% to efiectseparation of the fibrous product into a plurality of size fractions,one of which consists primarily of discrete whole ultimate fibers andflexible opened up bundles of the same having a particle size in therange of from +8 to 80 mesh particles as measured by a Clark Classifierand contains less than 5% of the +8 and less than 25 of the -80 meshparticles, entraining the said fraction in a moving gaseous vehicle,driving the component fibers While so entrained against a foraminoussupport member thereby forming a mat of impacted fibers in which theindividual fibers are randomly oriented and entrained by the drivingforce of the entraining vehicle, and consolidating the resulting mat bythe application of heat and pressure.

6. Fiberboard comprising essentially a hot bonded consolidated mixtureof vegetable fibers consisting pre dominantly of whole ultimate fibersand opened up aggregates of ultimate vegetable fibers containingsubstantially all of the organic substance of the vegetable matter fromwhich the fibers have been derived, the fiberboard having a density ofat least 30 pounds per cubic foot and interfiber bonds set at saiddensity, the component fibers of the fiberboard having a particle sizein the range of I from +8 to 80 mesh particles as measured by a ClarkClassifier and comprising less than about 5% by weight of the +8 andless than 25% of the 80 mesh particles, the said component fibers beinginterfelted in at least as great a degree as that characteristic of thesame fibers in substantially uniform 3-dimensional distribution at afelt-forming density of from 1 to 6 pounds per cubic foot and havingpositional relations relative to each other determined by the positionstaken by the fibers on compression of the felt.

7. Fiberboard comprising essentially a hot bonded consolidated mixtureof vegetable fibers consisting predominantly of whole ultimate fibersand opened up aggregates of ultimate vegetable fibers containingsubstantially all of the substance of the vegetable matter from whichthe fibers have been derived admixed with from about 0.1% to about 15%by weight of a cured thermosetting resin, the fiberboard having adensity of at least 30 pounds per cubic foot and interfiber bonds set atsaid density, the component fibers of the fiberboard having a particlesize in the range of from +8 to 80 mesh particles as measured by a ClarkClassifier and comprising less than about 5% by Weight of the +8 andless than 25% of the 80 mesh particles, the said component fibers beinginterfelted in at least as great a degree as that characteristic of thesame fibers in substantially uniform 3-dimensional distribution at afeltforming density of from 1 to 6 pounds per cubic foot and havingpositional relations relative to each other determined by the positionstaken by the fibers on compression of the felt.

8. Fiberboard comprising essentially a hot bonded consolidated mixtureof vegetable fibers consisting predominantly of Whole ultimate fibersand opened up aggregates of ultimate vegetable fibers containingsubstantially all of the substance of the vegetable matter from whichthe fibers have been derived admixed with from about 2% to about 60% byWeight of a thermoplastic resin, the fiberboard having a density of atleast 30 pounds per cubic foot and interfiber bonds set at said density,the component fibers of the fiberboard having a particle size in therange of from +8 to +80 mesh particles as measured by a Clark Classifierand comprising less than about 5% by weight of the +8 and less than 25%of r the 80 mesh particles, the said component fibers being interfeltedin at least as great a degree as that character istic of the same fibersin substantially uniform 3-dimensional distribution at a felt-formingdensity of from 1 to 6 pounds per cubic foot and having positionalrelations relative to each other determined by the positions taken bythe fibers on compression of the felt.

9. Fiberboard comprising essentially a hot bonded consoliated mixture ofvegetable fibers consisting of predominantly of Whole ultimate fibersand opened up aggregates of ultimate vegetable fibers containingsubstantially all of the substance of the vegetable matter from whichthe fibers have been derived admixed with from about 0.1% to about 15 byweight of a cured thermosetting resin and from about 2% to about 60% byweight of a thermoplastic resin, the fiberboard having a density of atleast 30 pounds per cubic foot and interfiber bonds set at said density,the component fibers of the fiberboard having a particle size in therange of from +8 to mesh particles as measured by at Clark Classifierand comprising less than about 5% by weight of the +8 and less than 25%of the 80 mesh particles, the said component fibers being interfelted inat least as great a degree as 15 that characteristic of the same fibersin substantially uniform 3-dirnensi0nal distribution at a felt-formingdensity of from 1 to 6 pounds per cubic foot and having positionalrelations relative to each other determined by the positions taken bythe fibers on compression of the felt. 5

References Cited in the file of this patent UNITED STATES PATENTS1,959,375 Loetscher May 22, 1934 10 16 Mason May 11, Heritage May 15,Ernst Oct. 30, Schubert et a1 Apr. 21, Fahrni June 16, Duvall July 21,

5. THE PROCESS OF MAKING CONSOLIDATED FIBROUS PRODUCTS WHICH COMPRISESDEFIBERIZING LIGNOCELLULOSE BY RUBBING AND ABRADING IT WHILECONTEMPORATANEOUSLY SUBJECTING IT TO AN ATMOSPHERE OF STEAM MAINTAINEDAT FROM ABOUT 50 TO ABOUT 200 POUNDS PER SQUARE INCH GAUGE ANDCORRESPONDING TEMPERATURES FOR SATURATED STEAM FOR PERIODS OF TIMERANGING FROM ABOUT 1/4 MINUTE TO ABOUT 30 MINUTES, THE LOWER LIMIT OFTHE PRESSURE-TEMPERATURE RANGE APPLYING TO THE HIGHER LIMIT OF THE TIMERANGE, MIXING WITH THE FIBROUS PRODUCT THUS PRODUCED FROM ABOUT 0.1% TOABOUT 15% BY WEIGHT OF THERMOSETTING RESIN AND FROM ABOUT 2% TO ABOUT60% BY WEIGHT OF THERMOPLASTIC RESIN, FRACTIONATING THE RESULTINGFIBROUS PRODUCT AT A MOISTURE CONTENT OF FROM ABOUT 5% TO ABOUT 40% TOEFFECT SEPARAONE OF WHICH CONSISTS PRIMARILY OF DISCRETE WHOLE ULTIMATEFIBERS AND FLEXIBLE OPENED UP BUNDLES OF THE SAME HAVING A PARTICLE SIZEIN THE RANGE OF FROM +8 TO -80 MESH PARTICLES AS MEASURED BY A CLARKCLASSIFIER AND CONTAINS LESS THAN 5% OF THE +8 AND LESS THAN 25% OF THE-80 MESH PARTICLES, ENTRAINING THE SAID FRACTION IN A MOVING GASEOUSVEHICLE, DRIVING THE COMPONENT FIBERS WHILE SO ENTRAINED AGAINST AFORAMINOUS SUPPORT MEMBER THEREBY FORMING A MAT OF IMPACTED FIBERS INWHICH THE INDIVIDUAL FIBERS ARE RANDOMLY ORIENTED AND ENTRAINED BYSOLIDATING THE RESULTING MAT BY THE APPRICATION OF HEAT AND PRESSURE.